| ||Front Cover|
| ||Results and discussion|
| Material Information
||Toxicity in plants due to copper from pesticides in tomato field soils
||NFREC, Quincy Research report
||9 leaves : ill. ; 28 cm.
||Rhoads, Fred ( Frederick Milton )
Olson, Stephen Michael
University of Florida -- Agricultural Experiment Station
||Florida Agricultural Experiment Station, Institute of Food and Agricultural Sciences, University of Florida
||Place of Publication:
||Plants -- Effect of copper on -- Florida ( lcsh )
Plants -- Effect of pesticides on -- Florida ( lcsh )
||government publication (state, provincial, terriorial, dependent) ( marcgt )
non-fiction ( marcgt )
||Statement of Responsibility:
||by F.M. Rhoads and S.M. Olson.
||Research report (North Florida Research and Education Center (Quincy, Fla.)) ;
|Table of Contents
Results and discussion
The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
NFREC, Quincy Research Report 90-2
Toxicity in Plants Due to Copper
University of Florida
Florida Agricultural Experiren Stations
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
UNIVERSITY OF FLORIDA
Copper containing pesticides are used in North Florida tomato
fields to control diseases that reduce yield and quality of the
local staked tomato crop. As much as 30 lb copper acre"1 may be
applied annually in cases of severe disease outbreak. Research
results show that once copper gets into the soil it moves very
little and tends to accumulate in the plow layer.
Symptoms of copper toxicity in commercial tomato crops in
North Florida have not been reported. However, symptoms of
suspected copper toxicity in oats following tomatoes were observed
in the fall of 1989. The literature does not contain extensive
information on copper toxicity in plants. Therefore, specific
symptoms of copper toxicity in tomatoes and oats were not found in
the literature. However, corn was reported to have reduced growth,
chlorosis of foliage, and stunted root development as a result of
copper toxicity. Tomatoes grown in pots of soil containing high
levels of copper exhibited reduced growth inversely proportional to
soil-copper content. Oats growing in a tomato field in the fall of
1989 exhibited severe foliage chlorosis where soil-copper level was
near 200 lb acre"1.
This report summarizes the results of a greenhouse experiment
with tomatoes growing in pots of soil containing varying amounts of
copper. In addition, soil-test and tissue-test results from a
field of oats following tomatoes and a field of oats where tomatoes
have not been grown are reported.
Two greenhouse experiments were conducted to determine the
effect of high soil-copper levels on the growth of tomato plants.
Tomato seedlings ('Sunny') were grown for six weeks in one-half
gallon pots of topsoil similar to that in most commercial tomato
fields. Copper hydroxide was added to the soil in experiment-i in
amounts ranging from zero to 5600 lb of copper acre"'. Calcite
(CaCO3) was added at rates of zero and 3.5 tons acre"' for each
level of copper in experiment-1. Rates of copper (as copper
hydroxide) in experiment-2 ranged from 0 to 1400 lb acre"' with lime
(CaCO3) levels at 0 and 7.0 tons acre"'. Each experiment contained
six rates of copper and two rates of lime for a total of 12
treatments with six replicates. Nutrient solutions containing
uniform levels of N, P, and K were added to each experiment to
maintain rapid growth.
At the end of a six-week growth period plant tops (cut at soil
surface) were harvested, dried, weighed, and analyzed for copper
content. Soil samples were collected from each pot after harvest
and Mehlich-I (extractant used in Florida extension soil testing
lab) soil copper and soil pH were determined.
Severe foliage chlorosis was observed in oats following
tomatoes in the fall of 1989. Soil samples were taken at two
depths (0-6 in and 6-12 in) at two locations (no symptoms and
severe symptoms) in the oats following tomatoes and in a field of
oats where tomatoes have not been grown. In addition, foliage
samples were taken at the same locations as the soil samples. Soil
and plant samples were analyzed for copper content and plant
samples were analyzed for nitrogen content.
RESULTS AND DISCUSSION
High copper rates reduced growth of tomatoes in experiment-i
without other visible symptoms (Fig. 1). Lime increased growth of
tomatoes at 350 and 700 lb of copper acre"'. However, lime did not
influence growth with the 1400 lb acre"' copper rate. Soil pH
ranged from 4.8 to 5.5 with no lime and from 5.9 to 6.5 with lime.
Data in Figure 2 are a combination of results from experiment-
1 and experiment-2. Liming to pH 6.5 neutralized the effect of
copper on growth of tomatoes at soil-copper rates less than 701 lb
acre-1. Growth of tomatoes was reduced more than 40% with a soil-
copper rate of 1400 lb acre"' at soil-pH levels between 6.5 and 7.2.
This suggests that lime cannot neutralize the effect of extremely
high levels of copper in the soil. The level of soil copper could
possibly surpass 1400 lb acre"' after 50 years of continuous tomato
production with annual applications of 30 Ib of copper acre"1.
Therefore, continued high rates of copper-containing pesticides
could create serious problems for future generations in the form of
Copper rates greater than 200 lb acre"1 produced maximum copper
concentration in tomato tissue (Fig. 3). A positive linear
response occurred between 0 and 208 lb copper acre"' and a linear
plateau response occurred above 208 lb copper acre"1. Tissue copper
was greater than 30 ppm in all cases of reduced growth due to
Cu Rate (Ib/acre)
Figure 1. Growth of tomato plants as a function of copper and lime rates.
M 700 Ib Cu/A lP 1400 Ib Cu/A
Relative Yield (%)
5.3 6.3 6.6 7.4 4.8 6.5 6.6 7.4 4.8 6.3 6.5 7.3 5.3 6.3 6.6 7.1
Figure 2. Growth of tomato plants as a function of copper rate and soil pH.
= 350 Ib Cu/A
M 0 Cu
A 0 Lime
Exp. 13.5 tons/acre
^g 3.5 tons/acre
r = 0.77
200 400 600 800 1000
Cu Rate (Ib/acre)
Copper concentration in tomato plant tissue
as a function of copper
Y = 12.8 +0.104X, if X < 208
Y = 34.3, if X = or > 208
copper toxicity but, plant growth was not reduced in all cases with
tissue copper greater than 30 ppm. Therefore, tissue copper level
is not a reliable index of copper toxicity.
Copper concentration in oat tissue was positively correlated
with extractable soil copper in the 0 to 6" soil layer (Table 1.).
The lowest copper concentration in oats (11 ppm) occurred with 3 lb
copper acre"' in the 0 to 6" soil layer. Oats with severe chlorosis
contained 32 ppm copper while growing in soil containing 192 Ib
copper acre"1. Plants with 18 ppm copper showed no toxicity
symptoms. Toxicity occurred in oats with a tissue level of copper
similar to that of tomatoes with reduced growth due to excessive
copper. Oats showing symptoms of toxicity were lower in nitrogen
but were not in the deficient range. This suggests that chlorosis
was not due to nitrogen deficiency.
Table 1. Copper and'nitrogen content of oat tissue and copper
content of soil samples from two fields.
Sample Oat Tissue Soil
Field area Cu N 0-6" 6-12"
ppm % -lb Cu/acre-
Oats (1) No symptoms 11 4.38 3 2
Tomato (2) No symptoms 18 4.30 56 -
Tomato (2) Severe symptoms 32 3.80 192 5
Extractable soil copper (sample from tomato field with
chlorotic oats) in the 0 to 6" layer was 192 lb acre'1 while the 6
to 12" layer beneath contained only 5 lb acre"'. When compared with
soil samples from a field where tomatoes have not been grown, this
represents a 64-fold increase in copper content for the 0 to 6"
layer and 2 1/2 fold increase for the 6 to 12" layer. Obviously,
copper is relatively immobile in the soil.
Ways to Reduce the Potential for Copper Toxicity
in Tomato Fields
1 Lime the soil to pH of 6.5 to 7.0. The
extension soil testing lab (University of
Florida) can determine lime requirement from a
soil sample for a specific soil pH.
2 Grow disease resistant varieties to reduce the
need for copper containing pesticides.
3 Rotate tomato crops between fields.
4 Deep plow to dilute the accumulated copper in
the 0-6" plow layer.